1. Field of the Invention
The present invention is directed to the field of forming insert members, and more specifically to headless insert members which are externally and internally threaded, the insert members being of the lobular, i.e. non-cylindrical, configuration.
2. The Prior Art
As conducive to an understanding of the present invention, it should be noted that the affixation of an insert member of the self-tapping type requires the application of substantial driving torque. It is known in the self-tapping screw art to provide, in lieu of a conventional cylindrical-bodied article, an article of lobular cross-section, (i.e. incorporating, in cross-section, portions which extend further from the longitudinal axis of the insert, separated by other portions closer to the longitudinal axis). Such inserts, after application to a workpiece, provide holding power nearly equal to the holding power of a cylindrical insert but may be applied with substantially lower driving torque, reduced incidence of chip formation etc.
By way of example, there is disclosed in U.S. Pat. No. 3,195,156 a self-tapping device of lobular cross-section, the device incorporating a driving head adapted to be engaged by a screw driver, chuck or the like, to provide the application of driving torque thereto. The noted patent describes a method or methods for producing the external threads of a formed lobular blank, which method involves interposing the shank portion of a formed blank between a pair of flat or curved thread forming dies which form an external thread simultaneously along the entire length of the blank.
The method in accordance with the noted patent requires that the blank be headed, relying upon the under surface of the head as a guide for locating the blank in the course of the thread formation. As a result, the procedure, while useful for forming headed, self-tapping members, such as screws, etc. is inapplicable, on any practical basis, for the formation of headless, self-tapping members, such as insert members.
While it is possible, of course, to take a formed headed fastener member fabricated in accordance with the method of the above referenced patent and thereafter sever the head, drill an internal bore and tap the bore to form an insert, it is obvious that such procedure is wasteful of material, and more importantly, requires the subjection of individual articles to sequential operations, with the attendant difficulties in handling.
As a result of the complicated and wasteful operations required to form lobular insert members in accordance with known methods, inserts commercially available have essentially universally been of the cylindrical type since cylindrical inserts may be readily manufactured using conventional techniques.
Thus, despite the known advantages of lobular construction and despite the availability of various headed self-tapping fasteners of lobular configuration, non-headed lobular inserts are, for all intents and purposes, commercially unavailable.